CRT: The Three-Lead Pacemaker

A three-lead pacemaker is a device that aims to bring the ventricles back to contracting in step in some patients with heart failure. Its medical name is CRT, cardiac resynchronisation therapy. What sets it apart from a conventional pacemaker is a third lead: it paces the left ventricle too, so that both ventricles contract at the same moment. It is not fitted in every patient with heart failure, though; suitability depends on the conduction problem on your ECG and on the pumping strength of your heart.

What Happens in Heart Failure?

Heart failure means the heart cannot pump blood with enough force to meet what the body needs. The commonest causes are a heart attack in the past, long-standing high blood pressure, valve disease and disease of the heart muscle.

Pumping strength is measured on the echocardiogram as the ejection fraction. It shows what percentage of the blood in the heart is pushed out with each beat. Normally that figure is above 55 per cent.

When it falls, breathlessness, tiring easily and swelling in the legs appear. Medicines are the basis of treatment; device treatments come alongside them, not in their place.

Left Bundle Branch Block: Contracting Out of Step

Some patients with heart failure have a second problem as well, and it is the starting point for CRT.

The heart’s electrical impulse spreads to the ventricles along two main routes: the right bundle branch and the left. Normally the two ventricles contract at almost the same moment.

If the left branch is blocked, the impulse reaches the left ventricle late. The right ventricle begins to contract while the left is not yet ready; part of the left ventricle contracts while another part is still relaxing. The contractions push against one another and force is wasted.

That delay is seen on the ECG as a lengthened QRS duration. The wider the QRS, the more marked the loss of step.

What Is a Three-Lead Pacemaker (CRT)?

The device is a conventional pacemaker with a third lead added:

• The first lead goes to the right atrium and follows the heart’s own rhythm.

• The second lead sits in the right ventricle.

• The third lead paces the left ventricle.

The device paces the two ventricles together, with calculated timing. The aim is to remove the delay and bring the contraction back into step. That is what the word resynchronisation describes: putting things back in time with one another.

The Road to Cardiac Resynchronisation Therapy

A device is not fitted as soon as heart failure is diagnosed. The decision comes at the end of a process with several stages. Knowing that process answers the question “why are we waiting?”

• Diagnosis and finding the cause. Behind heart failure there may be coronary artery disease, a valve problem, blood pressure or disease of the heart muscle. Where there is a correctable cause, that is dealt with first.

• Establishing the medication. The groups of medicines used in heart failure are started in stages and their doses increased slowly. This takes weeks.

• Waiting and measuring again. Once the medicines are at their optimal level, a period is allowed to pass and the echocardiogram is repeated. In some patients the pumping strength recovers during this time, and then no device is needed.

• Assessing the ECG. Where the pumping strength has stayed low, the QRS duration and the pattern of conduction are examined. The decision about a three-lead pacemaker takes shape here.

• Choosing the type of device. Resynchronisation alone, or a shock function as well? That decision follows your risk of a rhythm disorder.

These steps are not skipped. The benefit expected from the device only appears once the medication has settled into place.

Who Is a Three-Lead Pacemaker For?

What Is Looked For

• Symptoms of heart failure: breathlessness and limited exertion that persist despite medication.

• A low ejection fraction: usually 35 per cent or below.

• A wide QRS: a lengthened conduction time on the ECG. The longer it is, the clearer the expected benefit.

• Left bundle branch block: the benefit expected from CRT is greatest with this pattern of conduction.

• Optimal medication: the medicines must have been brought to their optimal level and a period allowed to pass.

That last point matters. In patients whose pumping strength recovers with medication, a device may not be needed. The decision is therefore not rushed.

It Is Not Fitted in Everyone

A low ejection fraction on its own is not a reason for CRT. If the QRS is narrow — that is, if there is no marked delay in conduction — the ventricles are already contracting in step. Adding a third lead to such a heart does not deliver the expected benefit.

The procedure is also postponed where another condition markedly shortens expected life span, where there is an active infection, or where heart failure treatment has not yet been brought to its optimal level.

CRT-P or CRT-D?

There are two kinds of device, and the difference is the shock function.

• CRT-P: resynchronisation only. It regulates the contraction and delivers no shock.

• CRT-D: it does the same, and carries an ICD function as well. It intervenes when a life-threatening fast rhythm develops.

Which suits you is decided by weighing the cause of your heart failure, your risk of a rhythm disorder, your age and your general condition together.

How Is the Device Fitted?

The procedure is done under local anaesthetic with sedation. A pocket is prepared under the skin below the collarbone and the leads are advanced through a vein to the heart.

Why Is the Third Lead the Difficult Part?

The first two leads are placed directly in the chambers of the heart. The left ventricular lead, though, does not go inside the heart but into the network of veins on its outer surface.

That network is entered through a common vein called the coronary sinus, and a suitable side branch is found. These branches differ in every patient; in some, finding a suitable one takes time.

Once the lead is placed, measurements are taken: is the impulse capturing the left ventricle adequately, and is a neighbouring nerve being stimulated? If it is not right, the lead is moved to another branch.

This stage is what makes a CRT procedure longer than fitting a conventional pacemaker.

Afterwards

Your arm movements are restricted for a period, which is needed for the leads to settle. The settings of the device are checked and discharge is planned.

The Detail That Decides It: the Percentage of Beats Paced

This section explains what determines whether CRT is working, and it is almost never set out on patient pages.

CRT only helps if it takes over on almost every beat. If the device is pacing only some of the beats, the ventricles go on contracting out of step for the rest.

At every review, therefore, a percentage is read from the device’s memory: on how many of the beats did it take over? That figure should be high.

The commonest reason for it falling is atrial fibrillation. Where the rhythm is irregular and fast, the heart’s own beats get ahead of the device.

The search for a solution goes like this: first an attempt is made to slow the pulse with medicines. If that is not enough, an ablation that removes the passage of impulses from the atria to the ventricles may be considered, so that the ventricles work only on the device’s impulse.

This is the concrete reason not to miss your reviews: that figure can only be seen by reading the device.

What Can Be Expected, and Does Everyone See It?

Setting the expectation correctly matters.

In carefully selected patients the goal is less breathlessness, more capacity for exertion and an improvement in the pumping strength of the heart. That change usually begins within weeks and can continue over months.

But it should be said honestly: not every patient sees the improvement expected. There are patients whose symptoms do not change noticeably although the device has been fitted.

The reasons include where the lead sits, the percentage of beats paced staying low, how widespread the scar tissue in the heart muscle is, and how far the underlying disease has progressed. In that case the settings are reviewed, the percentage examined, and the position of the lead reassessed if necessary.

Physiological Pacing: a Newer Approach

A different method has developed in recent years and is considered as an alternative to CRT in some patients.

In conventional CRT the left ventricle is paced from outside. In physiological pacing the lead is placed in the heart’s own conduction pathway instead. The aim is to spread the impulse along the heart’s natural route rather than an artificial one.

The contraction then happens in a pattern closer to the natural one. The method may be considered in patients where no suitable branch can be found through the coronary sinus, or who have not seen the benefit expected from conventional CRT.

Which method suits you is decided by assessing the conduction structure of your heart and how you have responded to earlier treatment.

How Do You Prepare?

• Screening for infection: because a permanent device and leads are being placed, there must be no active infection. A dental check is part of that assessment.

• Your list of medicines: bring everything you take, with the doses. Your doctor decides how blood thinners are managed.

• Your current ECG and echocardiogram: your QRS duration and your ejection fraction are the basis of the decision, so keep the reports with you.

• Your kidney results: contrast dye may be used during the procedure.

• Your expectations: what is and is not expected from the device is discussed beforehand, and your written consent is taken.

What Are the Possible Risks?

• Bleeding, bruising or swelling at the pocket

• Infection; one of the most serious problems in device treatment

• The left ventricular lead not being placeable, or moving out of position over time

• The lead stimulating a neighbouring nerve; noticed as a twitching in the abdomen and corrected by adjusting the settings or the position of the lead

• Injury to the lining of the lung or to a vessel while the leads are being placed; rare

• Fluid collecting in the sac around the heart

The risks are weighed against the benefit expected from the procedure and discussed in detail for your own situation at the consultation beforehand.

Follow-Up and Daily Life

• Reviews: the settings, the battery level and the percentage of beats paced are checked at set intervals. Remote monitoring systems can be used.

• The medicines continue. CRT does not take the place of medication. Dose changes are made by your doctor.

• Weight and salt: heart failure advice continues independently of the device. A sudden gain in weight can be a sign of fluid building up.

• MRI: a large proportion of devices today are MRI-compatible; always say so before a scan.

• Security gates and mobile phones: you can use them; tell the staff you have a device, and do not hold a phone very close to it.

• Activity: increased in stages; a cardiac rehabilitation programme may be recommended.

Three-Lead Pacemakers in Antalya

Prof. Dr. Umuttan Doğan is a cardiologist who trained in electrophysiology at the Gülhane Military Medical Academy in 2012; treating heart failure with CRT, and physiological pacing, are among the areas he works in. The procedures are carried out in the catheter laboratory at Antalya American Hospital.

If you have been diagnosed with heart failure and a device has been suggested to you, you can be seen at the clinic in Konyaaltı with your current ECG, echocardiogram and list of medicines. For the other device treatments see the pacemakers and leadless pacemaker pages. You will find his background and contact details on their own pages.

Frequently Asked Questions

What is the difference between CRT and an ordinary pacemaker?

A conventional pacemaker delivers an impulse when the heart beats more slowly than it should; its purpose is to maintain the rate. CRT takes over even where there is no problem with the rate; its purpose is to make the two ventricles contract at the same moment. A third lead paces the left ventricle for that.

Will CRT cure my heart failure?

CRT does not do away with the disease causing the heart failure. In carefully selected patients the goal is fewer symptoms and better pumping strength as the contraction comes back into step. Your medication and your reviews continue independently of the device.

The device is fitted but I do not feel better — what might be happening?

Not every patient sees the improvement expected. The first thing checked is on how many of the beats the device is taking over; if that figure is low, the reason is looked into. The position of the lead, the settings, any rhythm disorder and the state of the heart muscle are all weighed together. This is why it matters not to miss your reviews.

Are CRT and an ICD the same device?

No, but they can be combined. CRT regulates the contraction; an ICD intervenes in a life-threatening fast rhythm. A device carrying both is called a CRT-D. The kind that only resynchronises is called a CRT-P.

Will my medicines be stopped once CRT is fitted?

No. Heart failure medicines continue independently of the device and are generally kept at their optimal dose. Even if your symptoms ease, do not stop them on your own; your doctor decides on any change of dose.

The information on this page is for general guidance and does not replace a consultation. Decisions about diagnosis and treatment are made by your doctor after assessing your own situation.